Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r261916:

In sys/dev/xen/console/console.c, #if 0 an unused static function.

MFC r228631: kern cons: introduce infrastructure for console grabbing by
kernel

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Add support for alternative break-to-debugger support on the Xen console.
This should help debug boot-time hangs experienced in 9.0-BETA.

MFC after: 3 weeks
Tested by: sbruno
Approved by: re (kib)

A lack of console input is not the same thing as a byte of \0 input.
Correctly return -1 from cngetc when no input is available to be read.

This fixes the '(CTRL-C to abort)' spam while dumping.

MFC after: 3 days

remove annoying printf that cripples kdb on PV guests

Cleanups to the Xen console driver:

- Use CONSOLE_DRIVER() instead of the deprecated CONS_DRIVER() declaration.

- This means we cannot use cn_checkc anymore, which is supposed to do
the same as cn_getc nowadays. Remove the cn_getc implementation (that
was never being called) and rename cn_checkc to cn_getc.

- Don't run-time patch cn_putc, but add the logic to xc_cnputc().

This means I could do some cleanups to our console code...

Tested by: nobody on hackers@

Last minute TTY API change: remove mutex argument from tty_alloc().

I don't want people to override the mutex when allocating a TTY. It has
to be there, to keep drivers like syscons happy. So I'm creating a
tty_alloc_mutex() which can be used in those cases. tty_alloc_mutex()
should eventually be removed.

The advantage of this approach, is that we can just remove a function,
without breaking the regular API in the future.

Disable some un-needed console debugging.

don't acquire tty lock with console lock held

xen console lock needs to be a spin lock in case it is acquired from an interrupt context

Fix the Xen build for i386 PV mode.

Merge in support for Xen HVM on amd64 architecture.

merge 186535, 186537, and 186538 from releng_7_xen

Log:
- merge in latest xenbus from dfr's xenhvm
- fix race condition in xs_read_reply by converting tsleep to mtx_sleep

Log:
unmask evtchn in bind_{virq, ipi}_to_irq

Log:
- remove code for handling case of not being able to sleep
- eliminate tsleep - make sleeps atomic

Remove unused consdev structure fields.

The cn_unit and cn_tp fields don't seem to be used anywhere. Some
drivers set them, while others don't. Just remove them, in an attempt to
make our consdev code a little easier to understand.

Replace all calls to minor() with dev2unit().

After I removed all the unit2minor()/minor2unit() calls from the kernel
yesterday, I realised calling minor() everywhere is quite confusing.
Character devices now only have the ability to store a unit number, not
a minor number. Remove the confusion by using dev2unit() everywhere.

This commit could also be considered as a bug fix. A lot of drivers call
minor(), while they should actually be calling dev2unit(). In -CURRENT
this isn't a problem, but it turns out we never had any problem reports
related to that issue in the past. I suspect not many people connect
more than 256 pieces of the same hardware.

Reviewed by: kib

change netfront to match xen31_6
fix console locking

Integrate the Xen console driver.

I initially didn't want to integrate the Xen console driver, because it
did not receive any testing. Kip Macy suggested that I'd better check it
in right now, because this is the easiest way for him to test it while
he is working on the Xen import.

Requested by: kmacy

Compile fixes for xen build.

MFC after: 1 month.

Import Xen paravirtual drivers.

MFC after: 2 weeks